Astronomy

20 ASTRONOMY • JUNE 2018

common trick in

American football is

for a ball carrier to

take a quick step

forward in one

direction — making it appear

he’s heading that way — only to

change direction at high speed,

thereby confusing the defender

to avoid being tackled. It’s

called a “fake out,” and it not

only works on the playing field,

but also in the night sky with

some pretty shifty satellites.

A visual trickster

It doesn’t matter how skilled we

are as observers, satellites have

no shortage of visual tricks

to confuse our brain as they

sail across the playing field of

the night sky. While satellites

look like “stars” that move at a

steady clip in one direction, it’s

common for them to appear to

gently weave among the other

stars like a running back head-

ing for the end zone.

The slight weaving is a well-

known optical

illusion that

results from our

eye-brain sys-

tem. This com-

plex mass of

receptors and

nerves has dif-

ficulty fixing on

a moving point

of light (satellite) at night, espe-

cially when seen against a jum-

ble of other points of light (stars)

whose orientations change with

the turn of the head.

Now imagine the difficulty

the brain has in trying to keep

track of the path of a f lashing

or tumbling satellite, which we

only intermittently see as the

highly reflective metallic sur-

faces of these objects send

glints of sunlight to our eyes.

Spinning satellites (which cre-

ate rhythmic f lashes as the

craft rotates) are much easier to

follow than tumbling satellites

(such as rocket boosters and

space junk), which can f lash

erratically as they topple out of

control in a decaying orbit.

Sometimes, the f lashes are

so erratic in both magnitude

and frequency that tracking

their path requires a keen

knowledge of the night sky.

And therein lies the story of

my “running back” satellite.

A series of flashes

I have to applaud the rocket

booster or fragment of space

junk I saw recently because it

stopped me in my tracks with

its seemingly impossible move-

ments. Had I not persisted in

watching it with a critical eye,

I may have walked back in the

house scratching my head.

It started

with a pro-

longed, elon-

gated f lash

lasting long

enough for me

to detect its

direction

(along the

major axis of

the f lash). Scanning my eyes in

the direction of motion, I

waited for the next event. To

my surprise, it occurred well

below and to the right of the

first flash, causing me to

believe it was a different object.

The second f lash also was

elongated, and appeared to

travel perpendicular to the first

SECRETSKY

Satellite

‘fake out’

In honor of NFL

training camps

starting in July, let’s

compare an Earth-

orbiting satellite to

a running back.

satellite. So, now I had two

satellites to follow. A third

elongated f lash occurred in an

unexpected location in the sky,

followed by a fourth seemingly

unrelated flash.

The first photo-illustration

(above, top) shows the location

of the f lash (red), the direction

of elongation (white), and the

expected location of the next

event (yellow) for each object.

After the fourth f lash, however,

it became clear that the satellite

was, in fact, moving as it

should: on a straight and steady

course, but tumbling in a way

so that its rotation axis was not

aligned with its principal axis.

If the object itself were elon-

gated, like a rocket body, this

could explain the “fake out,” as

sunlight slid along the length

of the body. The second photo-

illustration (above, bottom)

shows that if you connect the

red dots, the satellite is indeed

moving along a straight line.

What’s interesting, however,

is that if you try to connect the

red dots with your eyes alone

in the first image, the red dots

seem to wiggle a bit. Perhaps,

as they say, it’s all in your head

(and mine!). As always, send

your thoughts to sjomeara31@

gmail.com.

BY STEPHEN JAMES O’MEARA

A

BROWSE THE “SECRET SKY” ARCHIVE AT http://www.Astronomy.com/OMeara.

The author added the colored dots, lines, and numbers to this photograph. The red dots

show where the flashes appeared to him. The white lines give the expected direction of

motion. The yellow dots show the expected location of the next event for each object.

This illustration

shows the true

path of the

satellite (the

red line) through

the stars.

Although the

events seemed

disjointed to the

author, the

appearance of

each flash (the

red dots in the

above image)

proves the object

was moving in a

straight line.

BOTH ILLUSTRATIONS: STEPHEN JAMES O’MEARA

Stephen James O’Meara

is a globe-trotting observer

who is always looking for the

next great celestial event.

Now imagine the

difficulty the brain

has in trying to keep

track of a flashing

satellite ...

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